The present invention relates to the field of optical switching in general and more particularly, to MicroElectroMechanical systems (MEMS) used in optical switching.
MicroElectroMechanical systems (MEMS) and devices have been recently developed as alternatives for conventional electromechanical devices, in-part because MEMS devices are potentially low cost, due to the use of simplified microelectronic fabrication techniques. New functionality may also be provided because MEMS devices can be much smaller than conventional electromechanical systems and devices.
In the area of optical switching, MEMS technology has been used to fabricate optical switches using MEMS reflectors, such as mirrors, to switch inputs thereto to selected outlets. Some MEMS reflectors in optical switches are moveable to provide the desired switch functions. For example, when a moveable reflector is moved to a reflecting position along an optical path, optical radiation that is conducted along the optical path can be reflected by the moveable reflector. When the moveable reflector is moved to a non-reflecting position outside the optical path, the moveable reflector may not reflect optical radiation from the optical path. Accordingly, moveable reflectors in optical switches can be positioned in reflecting or non-reflecting positions so that the optical switch can provide the desired switch functions.
It is known to fabricate xe2x80x9cpop-upxe2x80x9d MEMS reflectors to provide the moveable reflectors discussed above. For example, some pop-up reflectors have a non-reflecting position wherein the moveable reflector is positioned horizontally on an underlying substrate. When the moveable reflector is moved to the reflecting position, the moveable reflector rotates off the substrate (i.e., pops-up) to intersect the optical path. This type of pop-up reflector is described in further detail in U.S. application Ser. No. 09/489,264 to Wood et al., entitled MEMS Optical Cross-Connect Switch. 
In some MEMS devices using pop-up reflectors, the pop-up reflectors are aligned in the up position using a xe2x80x9cBed Of Nailsxe2x80x9d (BON) structure. The BON can provide an alignment structure so that when the pop-up reflector is moved to the up position, the pop-up reflector is accurately aligned to the optical path. In some MEMS devices, the BON is assembled with the underlying substrate including the pop-up reflectors. For example, the BON can be attached to the underlying substrate from above. Moreover, the BON is sometimes fabricated using relatively exotic starting material and may use Deep Reactive Ion Etching (DRIE) which can increase the costs associated with fabrication. The individual posts (or nails) in BON may also obscure some of the reflectors thereby increasing the difficulty to test and characterize the device.
In other types of MEMS devices, moveable reflectors are aligned without the use of the BON type structures described above. For example, in some types of MEMS, devices the moveable reflectors are moved over a relatively small angular range (i.e., less than 90 degrees) to different reflecting position. Such moveable reflectors can require relatively accurate positioning of the moveable reflector over the angular range. These types of moveable reflectors are discussed further in U.S. patent application Ser. No. 09/860,855, which is commonly assigned to the present assignee, Filed May 18, 2001 entitled Microelectromechanical Apparatus with Tiltable Bodies Including Variable Tilt-Stop Engaging Portions and Methods of Operation and Fabrication Therefor, the entire disclosure of which is hereby incorporated herein by reference.
It is known to control the angular position of the reflectors using voltages applied to planar control electrodes in the substrate and on the moveable reflector. A voltage applied across the planar electrodes can be used to develop an electrostatic force to control the position of the moveable reflector. Unfortunately, the electrostatic forces needed to position the moveable reflector can require relatively high voltages. For example, in some devices, voltages in excess of 150 Volts may be needed to accurately control the position of the moveable reflector. The use of such high voltages can increase the cost of MEMS devices due to the relative lack of availability of multi-port high voltage driver integrated circuits. Furthermore, the use of such high voltages can contribute to dielectric breakdown due to the relatively thin layers typically used in MEMS fabrication. Moreover, the use of planar electrodes for these types of moveable reflectors may require relatively large inter-electrode spacing which can reduce the xe2x80x9cfill factorxe2x80x9d associated with the MEMS device.
Embodiments according to the present invention can provide MEMS structures and methods of forming MEMS structure. Pursuant to some embodiments, a MEMS structure can include a recess in a substrate, the recess having a side wall and a floor. A tail portion of a moveable reflector is on the substrate and extends beyond the side wall opposite the recess floor and is configured to rotate into the recess. A head portion of the moveable reflector extends on the substrate outside the recess.
In some embodiments according to the present invention, the MEMS structures can include a latch member on the substrate that extends, opposite the floor, beyond a second portion of the side wall opposite the first portion of the side wall. The latch member holds the head away from the substrate to define a wedge shaped gap between the head and the substrate opposite the head.
In some embodiments according to the present invention, the moveable reflector is configured to rotate to a reflecting position wherein the tail contacts the side wall and the head is aligned with an optical radiation path parallel to the substrate in response to a magnetic force.
In some embodiments according to the present invention, the surface of the tail that contacts the side wall includes at least one raised structure thereon that keeps an adjacent portion of the surface from contacting the side wall.
In other embodiments according to the present invention, the moveable reflector pivots on the side wall and is cantilevered thereon to define a neutral position that avoids contact with the substrate. In some embodiments according to the present invention, a latch member extends from the side wall opposite the moveable reflector and contacts a portion of the moveable reflector to bias the moveable reflector into the neutral position. In some embodiments according to the present invention, the neutral position defines a non-parallel shaped gap between the moveable reflector and the substrate. In some embodiments according to the present invention, the non-parallel shaped gap comprises a wedge shaped gap.
Pursuant to method embodiments according to the present invention, a MEMS structure can be formed by forming a recess in a substrate, the recess having a side wall and a floor. A moveable reflector having a tail portion is formed on the substrate extending beyond the side wall opposite the recess floor and having a head portion extending on the substrate beyond the side wall outside the recess.
In some embodiments according to the present invention, a hinge is formed coupled to the moveable reflector and to the side wall to define an axis about which the moveable reflector is configured to rotate in a first direction into the recess to move the tail towards the side wall and to rotate in a second direction out of the recess to move the tail away from the side wall.
In some embodiments according to the present invention, a latch member is formed on the substrate extending, opposite the floor, beyond a second portion of the side wall opposite the first portion of the side wall. The latch member holds the head away from the substrate to define a wedge shaped gap between the head and the substrate opposite the head.